Vehicles are driven along routes set with navigation devices in some cases. Japanese Unexamined Patent Application Publication No. 2001-255167A discloses a device that, if a direction indicator of a host vehicle is not activated at an intersection to turn on a route, announces to the driver of the host vehicle that the direction indicator should be activated.
A vehicle turning at an intersection or changing a lane without activating a direction indicator is dangerous, and a collision between the vehicle and a vehicle traveling in the vicinity of the vehicle needs to be avoided.